Production of photographic stencils

ABSTRACT

573,798. Photographic wash-out reliefs. KODAK, Ltd., GRESHAM, D. C., and LOENING, E. E. Dec. 9, 1943, No. 20605. Drawings to Specification. [Class 98 (ii)] [Also in Group XXXVI] A stencil is produced from material comprising a light-sensitive layer comprising a hardenable colloid superimposed on another (preferably hydrophobic) layer more easily etchable than the former (when hardened) by exposure, dissolving away the image layer imagewise, and dissolving away the other layer in the areas laid bare with a bath which simultaneously etches the unhardened and less hardened parts of the upper layer but not the hardest parts thereof. The light-sensitive layer may be a gum-bichromate or silver halide emulsion layer. The lower layer may be soluble in acid baths, and the viscosity of the bath may be adjusted to obtain the best balance between the rate of the effect on the lower layer and that on the upper layer. If the light-sensitive layer is of gelatine emulsion, the imagewise solution may be performed with lactic acid, calcium chloride or magnesium chloride solution, or a mixture of glycerine, water, and sulphuric acid. The lower layer may be of shellac or &#34; Bakelite &#34; (Registered Trade Mark) and may be rendered insoluble after imagewise removal by baking. If the imagewise removal of the light-sensitive layer is performed in an acid bath, the other layer may be dissolved imagewise in an organic solvent. If the other layer is dissolved imagewise in an acid bath, the light-sensitive layer may be dissolved imagewise in warm water. Both layers may be removed imagewise in an acid bath, e.g. lactic acid to. which may be added ethyl lactate. Loading agents such as sodium sulphate may be added. The stencil may be produced on an electrically-conducting support which can be plated in the unprotected areas and the plated metal stripped from the support to produce a very fine grid, e.g. an electrical resistance. A thin sheet of copper may be nickel-plated and highly polished, coated with a thin layer of &#34; Bakelite &#34; soluble in lactic acid, coated with a layer of gum sensitized with potassium dichromate, exposed to a line positive of the desired grid, the unexposed portions washed away, the layer dried and treated with a mixture of lactic acid and ethyl acetate, the support made the anode in a copper-plating bath, the plate rinsed in water and made the cathode in a copper-plating bath, the gum and &#34; Bakelite &#34; removed by a solvent, and the grid stripped off. A lead design for use with X-ray exposures may be produced by coating a thin brass sheet on both sides with a layer of &#34; Bakelite &#34; soluble in lactic acid, coating both sides with bichromated gum, exposing both sides to the design in register, washing away the unexposed portions, dissolving the unprotected &#34; Bakelite &#34; in a lactic acid bath, drying, treating with aqueous lactic acid and immersing in a lead perchlorate plating bath between two lead anodes. The &#34; Bakelite &#34; layer may contain a colouring matter. A photolithographic printing surface may be produced by coating a zinc or aluminium plate with a solution comprising Bakelite &#34;, Sudan Red, acetone, and amyl acetate (and, if necessary, methylated spirit), overcoating with a gelatino-silver halide emulsion, exposing to a half-tone positive, developing in a tanning developer, removing the unhardened gelatine, drying, removing the unprotected &#34; Bakelite &#34; with lactic acid, and treating in a bath of nitric acid or ferric chloride to etch the bared metal. The exposed material may be developed in a non-tanning developer and the gelatine subsequently imagewise hardened. The process may be applied to line work. The plate may be processed by reversal by first developing in a non-tanning developer, washing, and developing in a tanning developer in the light, or a positive image may be obtained using an etch-bleach bath containing hydrogen peroxide. A graticule may be obtained by coating glass with a &#34; Bakelite &#34; layer, drying and warming to harden, overcoating with bichromated gum, exposing and removing unhardened gum and the &#34; Bakelite &#34; with a lactic acid bath (or first removing the unhardened gum. in a glycerine bath containing sulphuric acid and then the &#34; Bakelite &#34; in the lactic acid bath), and etching with hydrofluoric acid. Specifications 28415/07, 18775/08, [both in Class 98], and 473,446 are referred to.

1949- D. c. GRESHAM EI'AL 2,459,129

vnonucwxon 'OF PHOTOGRAPHIC snmcns Filed Nov. 30, 1944 -BICHROMATE D GUM 12 A PHENOL'FORMALDEHYDE RES/N ll N/CKEL PLATE J0 COPPER EXPOSED AND WASHED WITH WATER 1 fl 12 11 J0 TREATED WITH LACT/C ACID AND ETHYL AcETAT:

COPPER PLATED GUM AND RESIN REMOVED -DONALD C GRESI:L4M

ERICH E. LOENING INVENTORS BYQ M ATTORNEYS Patented Jan. 11, 1949 PRODUCTION. OF PHOTOGRAPHIC STENCILS Donald Charles Gresham and Erich Eduard Loening, Harrow, England, assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application November 30, 1944, Serial No. 566,027 In Great Britain December 9, 1943 The present invention relates to the production of stencils of a kind where a photographic relief image is formed in a layer coated on a, support which is usually metal and can subsequently be used for photolithographic printing or for metal plating, or glass etching or metal etching, e. g. for making half-toneblocks or graticules.

' Various methods have been proposed for producing such stencils. In some such processes a light-sensitive layeris coated directly on to the support of metal or the like, and an image formed in such layer which is then dissolved away imagewise. In such processes, especially when the image consists of fine clear lines in a resistant background, it is well known that diificulties are encountered when a sharp and accurately defined stencil is required. Other processes have been proposed to overcome such difficulties. Thus it has been suggested to use a substratum beneath the light-sensitive layer and after forming an image in the light-sensitive layer and removing it image-wise the parts of the substratum so laid bare are removed by for instance an ether-alcohol mixture if the substratum is collodion. The best known processes of this kind are described in British specifications Nos. 28,415 of 1907, 18,775 of 1908 and 473,446.

The present invention is directed to a method which enables still more sharply defined stencils to be produced whereby details can be reproduced which are finer than those which could be hitherto reproduced.

The accompanying drawing shows in sectional view an element at various stages in our process.

According to the present invention there is provided the method of producing a stencil wherein a light-sensitive layer comprising a colloid which can be hardened, is superimposed on another layer (preferably a hydrophobic layer) the latter being more easily etchable than the former (when hardened) and after exposure of the light-sensitive layer to an obj act or image it is dissolved away image-wise and the other said layer is dissolved away-in the areas so laid bare but not in the protected areas, characterised that image wise dissolving of the lower layer is performed by treatment with a bath which simultaneously etches the unhardened and less hardened parts of the upper layer but not the hardestparts thereof.

Preferably the lower layer is one which is soluble in acid baths, in which case the said bath is of an acidic character. The viscosity of the bath can be adjusted to obtain the best balance between the rate of the effect on the lower layer and I 2 Claims. (01. 204-41) 2 that on the upper layer. Usually the more viscous the bath the less is its effect on the upper layer relative to' that on the lower layer. For most purposes the viscosity of the bath should be at least 0.10 but preferably 0.25, such viscosity being measured according to Stokes law. For the best results the viscosity should usually be at least 0.35.

For the best results it is usually desirable that both layers be such as to be removed image-wise by means of an acidic bath. In the preferred form of the invention the image-wise removal of both layers is efiected simultaneously by a single treatmentin an acidic bath in which the soft parts of the layer which contains the light image andthe parts of the other-said layer thereunder are both soluble. 7

When the said other layer is one which is to be dissolved image-wise in acid it may be a, resin such as shellac, or a phenolformaldehyde resin which is soluble in lactic acid.

When the layer in which the image has been formed by light exposure is removed image-wise simultaneously with the image-wise removal of the acid soluble layer this can be done by means of lactic acid when the first mentioned layer is gelatine and the acid soluble layer is a phenolformaldehyde resin which is soluble in lactic acid. If pure lactic acid is employed then the rate of penetration of the top layer can be increased if desired by adding small amounts of water, e. g. 5 to 10% to the lactic acid; this addition of water should not be too great or otherwise the solution of the lower layer becomes inconveniently slow. Alternatively, .or in addition, small amounts of other liquids can be added, such as ethyl lactate to alter the rate of the imagewise solution. .i'To obtain the sharpest stencils it is advisable to maintain the lactic acid, or similar solution in a'relatively highly viscous state. For instance if an acid such as sulphuric acid is used to remove the said acid soluble layer, then it should be loaded very heavily with, for example glycerine with possibly a trace of water, for example we may use 9V2 parts of glycerine and part of sulphuric acid. Alternatively a loading agent such as sodium sulphate can be added.

If desired the stencil may be produced on an electrically conducting support which can be plated in the unprotected areas and then, if neces sary, the plated metal stripped from the support. Very fine grids can be made in this manner. It is'to be observed that to make an article, such as view an element used in our process and the appearance of the element at various stages in our process. As shown in the drawing, a copper plate l coated with a, layer of nickel II is coated with aphenoliormaldehyde resin I 2 and a bichromated gum or glue layer '13. After exposure of this element, preferably to a line image, it is washed with water to remove portions of the sensitive layer highly polished. It is then coated witha layer of a resin such as phenolformaldehyde resin which soluble in lactic acid. After the layer has been dried it is then coated with a layer of gum sensitised with potassium dichromate in the manner commonly used in photography. This sensitive gum layer is exposed to a line positive of the desired grid and the unexposed portions washed away in the usual manner. The layer is dried and then treated with a mixture of 90% lactic acid and ethyl acetate until the areas of the phe nolformaldehyde resin which are unprotected by the gum have been dissolved. The nickel plated support is then made the anode in a copper plating bath and a current of 40 ma. per square inch is passed for one minute. The plate is then rinsed in water and replaced as the cathode in the copper plating bath and a current of 40 ma. per inch is passed for minutes. This method of plating gives a thin copper foil which is subsequently stripped without difficulty from the nickel plated support. Before stripping, the gum and phenolformaldehyde resin may with advanbe removed by a solvent therefor.

The present invention can be applied to the production of designs in lead which are suitable for use in contact with sensitive silver halide layers during exposure thereof to X-rays in order to produce an image of the lead design onthe sensitive silver halide layer. To give a satisfactory image, the lead forming the design must be suiiiciently thick to have 'a high "degree of absorption for X-rays, A design of this kind can be produced as follows. 7

A thin brass sheet is coated on both sides with a layer of phenolior-maldehyde resin which is soluble in lactic acid. After these layers have been dried they are both then coated with a layer of a gum sensitised with potassium dichromate as in the previous example. These sensitive gum layers are both exposed to the design in register and the unexposed portion washed away as before leaving in register images of the design in hardened gum. The phenolform'aldehyde resin which is unprotected is, as before, dissolved in a lactic acid bath and the stencils so formed are dried.

The plate may then be treated with a bath made of equal parts of lactic acid and water (by volume) to remove any surface stain and then rinsed. The plate is then immersed in a lead-perchlorate plating bath between two lead anodes for 16 hours at a current density of 0.034 ampere per square c. These plates lead on to both sides of the plate so that twice the thickness of lead can be obtained than if only one side were treated. If there is any tendency to produce lead trees during plating these can be removed by gentle brushing during interruption of the plating. A thickness of lead of 0.25 mm. on each side of the brass support can be obtained while still maintaining a sharp image of the original design.

The phenolformaldehyde resin layer may, if desired, have a colouring matter incorporated in it when it is first coated, since this facilitates subsequently inspection or the image-wise solution thereof.

The accompanying drawing shows in sectional t3 as shown at M. The element is then treated with a mixture of lactic acid and ethyl acetate to etch out the phenolformaldehyde resin where the bichromated layer has been washed away as shown at I5. The element thus produced is used to form agrid, for example of copper, by electroplating copper on it, the copper adhering only in the unexposed portions as shown at IB. After removal of the resin and gum layers l2 and 13,

the copper grid 16 remains as shown in the last step of the drawing and can be stripped from the layer 1 l to form the completed grid.

The present invention can be applied to the production of glass-etched graticules. Thus the surface of a piece of glass may be first coated with a layer of a phenolform'aldehyde resin as before given, using, for instance, the following mixture containing Sudan Red,

Phenolformaldehyde resingrams '20 Sudan Red (Rowes 'Color Index No.

857) l grams 5 Acetone ..cc. '90 Amy] acetate -cc 10 If desired, this layer can after drying be hardened somewhat by warming it. A layer of gum sensitised with potassium bichromate is coated thereover and dried. After exposure the unhardened gum and the phenolformaldehyde resin thereunder can be removed in a bath of lactic acid. Alternatively, the unhardened gum can be first removed in, for example, glycerine containing a small amount of an acid such as sulphuric acid and then the unprotected areas of the phenolformaldehyde resin removed by lactic acid.

The glass bearing the phenolformaldehyde resin stencil so obtained is then treated with an etching solution, such as hydrofluoric acid, in the usual way. If desired, the phenol'formaldehyde resin stencil can, before this etching, be hardened by heating.

What we claim is:

l. The method of producing a stencil in an element comprising a support, a first phenoliorm'aldehyde layer carried thereby, and a second light-sensitive bichromated glue layer superimposed thereon comprising the light printing of an image in the second layer and the transforma tion of said light image to 'a hardened relief image, characterized by the treatment of said element after formation of said relief image, with an etching bath of lactic acid and 10% ethyl acetate that etches any un'hardened portions of the outermost layer and also the portions of the first layer exposed through said relief image.

The method of making an electrical resistance consisting of a fine metallic grid that comprises printing an image of line lines upon an element comprising a nickel-plated copper support and two superimposed layers thereon, the inner layer being a phenolformaldehyde resin composition and the outer layer being light-sensitive bichromated glue, transforming the image in the outer layer into a hardened relief image, treating the element with a bath of 90% lactic acid and 10% ethyl acetate that attacks any unhardened portions o'f'the outer layer and the por- Bekk Apr. 28, 1931 Name I Date Gundlach Aug. 15, 1933 Funck May 18, 1937 Beynen 'et a1 July 12, 1938 Norris July 18, 1939 Meulendyke Sept. 17, 1940 Beebe Dec. 24, 1940 Wood Sept. 30, 1941 Holman Apr. 14, 1942 Toland Oct. 31, 194 1 FOREIGN PATENTS Country Date Austria Feb. 10, 1912 Great Britain. Nov. 15, 1923 Great Britain June 19, 1942 

